Add .frt samples for Forth.

samples/Forth/bitmap.frt

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+\ Bit arrays.
+: bits ( u1 -- u2 ) 7 + 3 rshift ;
+: bitmap ( u "name" -- ) create bits here over erase allot
+   does> ( u -- a x ) over 3 rshift +  1 rot 7 and lshift ;
+: bit@ ( a x -- f ) swap c@ and ;
+: 1bit ( a x -- ) over c@ or swap c! ;
+: 0bit ( a x -- ) invert over c@ and swap c! ;
+: bit! ( f a x -- ) rot if 1bit else 0bit then ;

samples/Forth/enum.frt

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+\ Implements ENUM.
+
+\ Double DOES>!
+: enum   create 0 ,  does> create dup @ 1 rot +! ,  does> @ ;
+
+\ But this is simpler.
+: enum   create 0 ,  does> dup @ constant 1 swap +! ;

samples/Forth/macros.frt

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+\ Simplifies compiling words.
+
+: [[     ; immediate
+: '<>    >in @ ' swap >in ! <> ;
+: (]])   begin dup '<> while postpone postpone repeat drop ;
+: ]]     ['] [[ (]]) ; immediate
+
+( Usage:   : foo ]] dup * [[ ; immediate   : bar 42 foo . ; )